Sonar tracking of unknown possible objects

ABSTRACT

Reflected sonar signals arising from one or more possible unknown objects are distinguished according to a first criterion, and possible shapes each having a defined unique associated point are assigned each of the possible unknown objects. Then the three dimensional points are tracked by the sonar system.

FIELD OF THE INVENTION

The field of the invention is the field of visualization and use of datafrom sonar signals scattered from sparse objects immersed in a fluid.

RELATED PATENTS AND APPLICATIONS

The following US Patents and US patent applications are related to thepresent application: U.S. Pat. No. 6,438,071 issued to Hansen, et al. onAugust 20; U.S. Pat. No. 7,466,628 issued to Hansen on Dec. 16, 2008;U.S. Pat. No. 7,489,592 issued Feb. 10, 2009 to Hansen; U.S. Pat. No.8,059,486 issued to Sloss on Nov. 15, 2011; U.S. Pat. No. 7,898,902issued to Sloss on Mar. 1, 2011; U.S. Pat. No. 8,854,920 issued to Slosson Oct. 7, 2014; and U.S. Pat. No. 9,019,795 issued to Sloss on Apr. 28,2015; U.S. patent application Ser. Nos. 14/927,748 and 14/927,730 filedon Oct. 30, 2015, Ser. No. 15/978,386 filed on May 14, 2018, Ser. No.15/908,395 filed on Feb. 28, 2018, and Ser. No. 15/953,423 filed on Apr.14, 2018 by Sloss are also related to the present application. The aboveidentified patents and patent applications are assigned to the assigneeof the present invention and are incorporated herein by reference intheir entirety including incorporated material.

OBJECTS OF THE INVENTION

It is an object of the invention to improve the tracking of unknownpossible objects using sonar imaging. It is an object of the inventionto measure and record the positions and orientations of possible objectswith unknown shapes. It is an object of the invention measure theincrease or decrease in the probability that a possible object is a realobject as the possible object is tracked. It is the object of theinvention to refine the measurements of the shapes of unknown objectsover time while the objects are tracked.

SUMMARY OF THE INVENTION

One or more large arrays of sonar detectors are used to produce threedimensional sonar images possible unknown objects. A series of sonarpings are sent into an insonified volume of water and the reflected orscattered sonar pings are analyzed to produce a 3 dimensional map ofpoints which have scattered the sonar ping. The points are segregated byone or more techniques, and one of a defined set of shapes is assignedto each segregated set of points. Each of the defined set of shapes hasan associated defined unique 3 dimensional position and possibly adefined spacial orientation. For each ping, the defined position isrecorded and tracked from ping to ping to provide a record of the trackof the defined shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows of a cable laying vessel laying cable to a sea bed.

FIG. 2 shows a flow chart of a manually controlled cable measuringsystem.

FIG. 3 shows a flow chart of an automatically controlled cable measuringsystem.

DETAILED DESCRIPTION OF THE INVENTION

It has long been known that data presented in visual form is much betterunderstood by humans than data presented in the form of tables, charts,text, etc. However, even data presented visually as bar graphs, linegraphs, maps, or topographic maps requires experience and training tointerpret them. Humans can, however, immediately recognize andunderstand patterns in visual images which would be difficult for eventhe best and fastest computers to pick out. Much effort has thus beenspent in turning data into images.

In particular, images which are generated from data which are notrelated to light are often difficult to produce and often require skillto interpret. One such type of data is sonar data, wherein a sonarsignal pulse is sent out from a generator into a volume of fluid, andreflected sound energy from objects in the insonified volume is recordedby one or more detector elements. The term “insonified volume” is knownto one of skill in the art and is defined herein as being a volume offluid through which sound waves are directed. In the present invention,a sonar signal pulse of sound waves called a ping is sent out from oneor more sonar ping generators, each of which insonifies a roughlyconical volume of fluid.

The field of underwater sonar imaging is different from the fields ofmedical ultrasonic imaging and imaging of underground rock formationsbecause there are far fewer surfaces in the underwater insonifiedvolume.

FIG. 1 shows a sketch of a vessel 10 Ultrasonic sonar generators or pinggenerators 15 suspended in the water emit ultra sonic sound waves 16which strike objects or possible objects 11 and 17 in the volume or onthe seafloor. The ultrasonic ping generators 15 are attached to or arein proximity to large array multielement sonar receivers (not shown) forreceiving reflected sonic waves.

The sonar generators 15 may be attached to or in a known location inproximity to one or more of the vessels 10, or to one or more mobileunderwater probes 19. Sound waves 18 are shown reflected from possibleobjects 11, 12 and real objects 17 back towards the one or moremultielement sonar detectors. Objects and possible objects may besuspended in the water, lying on the seabed 12, or be buried in the seabed 12. Objects 17 may be both real and known. A known object is anobject with a known shape which has been previously identified andimaged, and can be recognized by the sonar imaging system or a skilledoperator. Objects 11 are not immediately recognized as real, and may bespurious collections of reflections and re-reflections. Objects 12 maybe one object or two. None of these possible objects can be classed asreal immediately. They are affectionately known as “blobs”.

However, all segmented possible objects must be treated as if they arereal for the purposes of tracking.

The method of the invention starts out be choosing a defined known shapefrom a set of defined shapes to assign to each of the blobs. In thepreferred method of the invention, the simplest mathematical shape whichcan be used is a sphere of radius r. We assign a position to each of thedefined shapes in order to locate the defined shape.

For the sphere, we choose the center of the sphere as the assignedposition for the spherical shape. In general, we calculate the center ofmass for each shape as if the assigned shape were filled uniformly withmaterial of constant density. We then choose the position of the centerof mass as the position of the shape for the purposes of tracking.

We call the center of mass point a centroid. The next simplest shape isan ellipsoid. having a centroid position determined as the point halfwayalong the major axis. The orientation of the ellipsoid, in contrast to asphere, can be recorded as the angular coordinates of the major axis.More complicated shapes may need two angular coordinates as well asthree spatial coordinates.

Any number of defined shapes can be used, such as cylinders with squareends, cylinders with half spherical end caps, partial cones, etc. Eachdefined shape has its unique point defined. We call the assigned pointthe centroid of the shape.

The method of the invention uses a series of pings to assign a point foreach blob for each ping.

The points are recorded, and can be plotted in 3 dimensional space as afunction of time for tracking purposes. As more data is gathered, theshapes may become better defined, and a new shape chosen to betterfollow and track the object. Some of the objects may even coalesce intoone shape, or one shape will break into two or more shapes depending onsuch things as the sonar reflectivity over the surface of the shape. Asthe shapes become better known, centroids can be calculated for themalso without using the defined set of shapes.

Points may be associated with each shape other than the calculatedcenter of mass. The most preferred method of the invention is to use thecentroid of the defined shape.

The ultrasonic multielement sonar detectors measure the phase,intensity, and arrival time of the reflected sonar pings 18. The phase,intensity, and arrival time data are processed to provide threedimensional location data measuring sonar reflecting surface locations.The seabed 12 surface and the object 17 surface may be similarlymeasured to give three dimensional location data of the reflectingsurfaces.

A series of outgoing ping pulses may be sent out with an outgoing pingfrequency P_(f). A sonar ping generally has a constant sound frequencyf.(The frequencyf is sometimes changed in the prior art during the ping ina method called a chirped pulse ping, where the pulse frequency eitherincreases or decreases monotonically throughout the pulse.) A masteroscillator (not shown) produces a square wave voltage output atfrequency f, and the ping generator uses the master oscillator toproduce outgoing sinusoidal sound waves in phase with the masteroscillator.

The reflected sound waves 18 are received by each detector element oneor more of the large multielement sonar detector arrays associated witheach ping generator 15. The detector arrays measure the pressure vs timeof the reflected ping sound waves at each element and return an analogelectrical voltage signal representing the amplitude versus time of thesound wave impinging on the element. The electrical voltage signals aredigitally sampled at precisely known times with respect to the phase ofthe sent out sound waves of each ping. A large array multielementdetector is preferably constructed with 24 by 24 or more sonar detectorelements arranged orthogonally as a square grid. A two dimensional sonardetector array which has m by n elements, where m and n are differentintegers will have different angular resolutions in two orthogonalangles.

The attenuation of the sent out and received sonar signals is dependenton the sent out frequency P_(f). As the frequency P_(f) increases, thesonar resolution increases and the detection range decreases. Thefrequency P_(f) may be changed from ping to ping to either see furtherat the expense of resolution, or to see more detail of the closer soundreflecting objects. A skilled operator is needed for manual control ofthe ping frequency P_(f), or an computer programmed to change frequencyP_(f) according to a criterion, such as the need for higher resolutionor greater range

The amount of raw digital data generated by large array sonar detectorsis often too great either to transmit to the surface vessel from thearray detector or to store for later analysis. This is especially truefor independently operated probes without high speed data connections tothe vessel 10. In these cases, the raw data must be analyzed close tothe detector, so that signals representing the various tracks may besent to the control vessel may be sent by low bandwidth means such assound waves.

Independently operated ROV (remotely operated vehicles) are especiallysuited for using the method of the invention. They may be small enoughto be less easily detected than manned vehicles. Such remotely operatedvehicles must be programmed to make many decisions according to variouscriterion.

For example, the decision to switch from a spherical shape to anellipsoidal shape could use the criterion that the raw data points couldbe contained in a ellipsoid with major to minor axis ratios greater than1.5. Other such criterion are noted in Appendix I.

Flow charts of the invention are shown in Appendix I for manually andautomatically carrying out the method of the invention. A skilledoperator is usually carried by the cable laying vessel 10. Thealgorithms automatically distinguishes/segments signals from thesea-bed. Using sonar data describing More flowcharts describing theinvention are described in Appendix I

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

We claim:
 1. A method of sonar tracking of possible unknown objects in avolume of fluid, comprising: a) directing a first one or a first seriesof pulsed sonar beams into the volume of fluid, wherein the one or thefirst series of pulsed sonar beams is produced by a pulsed sonar beamgenerator in communication with the volume of fluid; b) receiving sonarsignals from the volume of fluid, wherein the received sonar signals arereceived by a sonar signal receiver; c) analyzing the received sonarsignals, wherein the analysis is performed with a first analysis method;then d) distinguishing sonar signals arising from reflections of thefirst one or the first series pulsed of sonar beams from one or morepossible unknown objects, wherein the sonar signals are distinguishedaccording to a first criterion; then e) assigning first possible shapesto the one or more possible unknown objects according to a secondcriterion, wherein each of the first possible shapes have a definedunique associated point; then f) calculating three dimensionalcoordinates of the defined unique associated points.
 2. The method ofclaim 1, wherein a description of the first possible assigned shapes andthe calculated three dimensional coordinates of the defined uniqueassociated points are communicated.
 3. The method of claim 1, furthercomprising; g) changing zero or more characteristics of the pulsedenergy beam producer, the energy receiver, or the analysis method,wherein the characteristics are changed in response to the analysis ofstep c) according to a third criterion.
 4. The method of claim 1,further comprising; h) directing a second one or a second series ofpulsed sonar beams into a volume of fluid, then repeating steps b)through f); then; g) calculating new three dimensional coordinates ofthe first possible shapes of the one or more possible unknown objects;then. h) calculating the rate of change of the three dimensionalcoordinates.
 5. The method of claim 4, wherein the rate of change of thethree dimensional coordinates is communicated.
 6. The method of claim 4,wherein a description of the real time track of the three dimensionalcoordinates with time is stored.
 7. The method of claim 4, wherein thefirst possible shapes of the one or more possible unknown objects arereassigned to second possible shapes according to the results ofrepeating steps a) through f), the reassignment carried out according toa criterion, and calculating three dimensional positions of the uniqueassociated points of the second possible shapes.
 8. The method of claim7, wherein the reassigned second shapes are used to replace the firstshapes in previous calculations, and a new track of the uniqueassociated points of the second shapes is recorded.
 9. A method of sonartracking of possible unknown objects, comprising: a) directing a firstone or a first series of pulsed sonar beams into a volume of fluid,wherein the one or a first series of pulsed sonar beams is produced by apulsed sonar beam generator in communication with the volume of fluid;b) receiving sonar signals from the volume of fluid, wherein thereceived sonar signals are received by a sonar signal receiver; c)analyzing the received sonar signals for each of the first one or eachof the first series of received pulsed energy signals, wherein theanalysis is performed with a first analysis method; then d)distinguishing sonar signals arising from reflections of sonar beamsfrom one or more possible unknown objects, wherein the sonar signals aredistinguished according to a first criterion; then e) assigning threedimensional positions to the one or more possible unknown objectsaccording to a second criterion, wherein the positions are not assignedon the basis of an edge detection technique.
 10. The method of claim 9,wherein a description the calculated three dimensional positions arecommunicated.
 11. The method of claim 9, further comprising; g) changingzero or more characteristics of the pulsed energy beam producer, theenergy receiver, or the analysis method, wherein the characteristics arechanged in response to the analysis of step c) according to a thirdcriterion.
 12. The method of claim 9, further comprising repeating stepsa) through e); then; f) calculating the new three dimensional positionsof the one or more possible unknown objects; then, g) calculating thethree dimensional rate of change of the positions.
 13. The method ofclaim 12, wherein a description of the three dimensional rate of changeof the positions with time is communicated.
 14. The method of claim 12,wherein a description of the real time track of possible positions withtime is stored.
 15. The method of claim 12, wherein a description of thereal time track of possible positions with time is communicated.